Friday, May 3, 2019

Discussion: Getting Rid of 9V Batteries for my Pinpointer

LiPo with 9V voltage booster for Minelab Pro-Find 35

I really like batteries, with the exception of the 9V battery. It’s expensive and has poor performance with respect to its internal resistance and capacity. In my opinion, nothing designed after 2010 should be using a 9V battery. Maybe some of you out there can think of a reason as to why a particular device, such as a multimeter or smoke detector should still use a 9V battery, but I doubt that’s possible. And if it is possible, it will be an exception.

I also enjoy metal detecting. However, my metal detector (Fisher Research Labs F2) and pinpointer (Minelab Pro-Find 35) both use 9V batteries. My next metal detector will use AA (Garrett AT series or Fisher F75) or a built in lithium (a la Minelab Equinox), but until then, I’m stuck with 9V batteries…or so I thought.

What’s a Pinpointer?

For you readers out there that aren’t familiar with metal detecting, a pinpointer is a handheld device that helps pinpoint a metal object in a hole or plug you just dug. You don’t have to have it while metal detecting, but it saves a lot of time.

The majority of the pinpointers on the market today use 9V batteries. The three major exceptions are Fisher Research Labs’ F-Pulse, White’s Bullseye TRX and XP’s MI-4 and MI-6.

I set out to create an add-on that would allow my Pro-Find 35 to use something other than a 9V battery. This blog post sets out how I did it.

The Set up

A picture is worth a 1,000 words, so I’ll start with pictures (they're upside down for some reason).

The connectors I’m using are Deans and the blue thing on the right is the voltage booster itself. Here are some of its more notable specs and pics:

Minimum operating voltage: 2.5v
Weight: 0.4g
Maximum quiescent current: 2ma
Minimum input current: 1.4a
Switching frequency: 1.3 khz (PWM control)

Here’s a link to where the item itself, in case you want to order one or learn more about it:

Below are some pictures of it installed in my pinpointer:


I have not tested this in real world conditions, just indoors using the “hour glass and coin” method. Below you can see how it performs with the stock 9V battery:

I didn’t mark the cardboard, but when using the nickel and the voltage booster, the sensitivity improved by about 1-3 mm, i.e. the hourglass enlarged by about 1-3 mm in all directions except the middle bottleneck.

As for run time, that depends on the battery used. I’m currently using what’s in the pictures and it has 750mah in capacity at 3.7 nominal volts. Fully charged it’s around 4v. Using some rough math, this voltage booster is the rough equivalent of a 9V battery with 330mah of capacity. The typical 9V alkaline battery has about 550mah. Therefore, you can expect about 60% of the run time of whatever you’d get with an alkaline 9V battery. But there are at least two caveats to my numbers.

First, the efficiency of the voltage booster. I don’t know what it is, but I wouldn’t be surprised if it’s around 85%-90%. If I’m wrong, feel free to comment.

Second, the relatively low resistance of my set up. When using the stock 9V battery (it’s heavy duty, not alkaline), the battery has trouble delivering the current necessary when the pinpointer goes off. I know this because the LED slightly blinks rapidly. But this voltage booster set up does not result in the LED light slightly blinking at all.

I think my use of a much higher performing battery than the 9V battery (heck, almost any battery will do better than a 9V) at least partially compensates for the efficiency loss of the voltage booster. I think this compensation effect will still exist when using an alkaline battery instead of a heavy duty, although the effect will be less.

What Are the Advantages and Disadvantages of the 9V Booster?

The sole advantage is that you don’t need to use 9V batteries any more. This can make organizing your battery supply that much easier and save money on an expensive battery type. For some of you metal detectorists out there, this might allow you to completely remove 9V batteries from your metal detecting set up.

Numerous disadvantages include:

- You need a special charger. A typical R/C hobby style charge that can handle LiPo cells should suffice.
- It’s a bit janky, at least compared to a self-contained 9V battery. I intend to clean things up a bit as I tweak this design. I should be able to get most of everything to fit inside a gutted 9V battery.
- At least slightly lower capacity/run time. I don’t know this for sure, but I will assume this is the case for now. Under real world conditions, I wouldn’t be surprised if the run time is about the same with my 1S 750mah LiPo battery.
- If you want to avoid using a special charger and use drop-in AAA cells, you need to permanently modify your pinpointer. In my case, I’d need to cut a large hole in the end cap and effectively lengthen it to accommodate the AAA battery holder like this one:

It won’t be hard to do, but I don’t want to do anything to permanently modify my pinpointer while it’s under warranty.

Bottom Line

For most of you, it won’t be worth using this voltage booster. If you already have a hobby R/C charger and soldering tools and supplies, then you might enjoy this little project and can save some money in the long run by getting rid of 9V batteries

But if you hate 9V batteries as much as I do, you’ll definitely want to consider this.

Sunday, March 3, 2019

Discussion: Epinephrine Autoinjectors

Attribution: Jfoldmei per Creative Commons Attribution-Share Alike 3.0 Unported license.

Disclaimer: I’m not a doctor. Please use the following blog post for informational purposes only and not as medical advice. Any questions or concerns should be directed to your doctor or other appropriate medical professional.

Epinephrine autoinjectors (sometimes referred to as the brand name, EpiPen) aren’t the typical outdoor gadget, but for some with severe allergies, it might be the single most important thing they take with them when they head to the outdoors or leave the house (well, except for maybe their keys and phone).

I’ve recently taken a fascination with these marvels of engineering and I want to take this opportunity to provide a brief overview of epinephrine autoinjectors for those who might be confused, curious or seeking more information about something they have to carry everywhere they go.

What’s an Epinephrine Autoinjector?

An epinephrine autoinjector is a unique type of syringe that automatically injects epinephrine into an individual. Unlike a regular syringe, autoinjectors are special because they already have a preloaded dose of medication and contain an internal mechanism that allow the user to inject the medication without having to see the needle or press down on a plunger.

In the United States, epinephrine autoinjectors usually come in two doses: 0.3 mg for adults (or anyone weight 66 pounds or more) and 0.15 mg for children (or anyone weighing between 33 and 66 pounds). There’s also a 0.1 mg dose for infants and toddlers (or anyone weighting between 16.5 and 33 pounds), but it’s not as common.

Why Do We Have Epinephrine Autoinjectors?

The primary purpose of epinephrine autoinjectors is to deliver an emergency injection of epinephrine (also known as adrenaline) to an individual suffering a severe allergic reaction, specifically anaphylaxis. Anaphylaxis has a variety of symptoms, but the most serious include swelling of the throat, fainting and trouble breathing. In rare cases of anaphylaxis, death can occur.

For more information about anaphylaxis, I encourage you to check out the following online resources:

Types of Epinephrine Autoinjectors Available

A few years ago, there was pretty much just one option for anyone looking for an epinephrine autoinjector: the EpiPen. Now, there are many more options, most of which are cheaper. I’ll go over most of the epinephrine autoinjector options available (or soon to be available) in the United States.

Amedra Pharmaceutical’s Adrenaclick

Caption: Adrenaclick with 0.15 mg dose

To be honest, I don’t think this is still available for sale in the United States and if so, I don’t know how easy it will be to obtain. But I still want to mention it because it’s closely related to a current and past version of an epinephrine autoinjector.

The past version is the Twinject. I don’t know the exact relationship between the Twinject and the Adrenaclick, but they are based on very similar designs. What made the Twinject special was that it has an internal syringe could be removed to provide a second dose of epinephrine if necessary.

Caption: Twinject, “adult” version with the 0.3 mg dose.

The current version of the Adrenaclick is its generic equivalent. Who makes it is a bit confusing, but I think it’s either Impax, Lineage or Amneal. My understanding is that Impax acquired the rights to Adrenaclick and then merged with Amneal. And Lineage is (was) a whole-owned subsidiary of Impax. You can see what it looks like below:

Caption: Generic version of the Adrenaclick in both the 0.15 mg and 0.3 mg doses

With some MacGyver-ing, you can get a second dose of epinephrine relatively easily from the generic version of the Adrenaclick (and the EpiPen). Just keep in mind this is an improper (and possibly illegal? I don’t know) use of this medication. But in an extreme emergency where medical care is hours or days away and a second injection is needed, it’s an option.

Mylan’s EpiPen

Just to set the record straight or clear up any confusion, “EpiPen” is the brand name of a particular type of epinephrine autoinjector. Specifically it’s the epinephrine autoinjector made by Mylan. Many people, including doctors, will use the term EpiPen to reference any epinephrine autoinjector.

If the name and device sounds or looks familiar, it’s because they got a lot of bad press recently about price hikes on the EpiPen when there was no alternative available and many customers felt like they were being price gouged. Whether Mylan was acting unethically or were just acting as a business savvy company, I’ll leave it up to you to research and decide on your own.

Caption: The older version of the EpiPen. Its overall design might look familiar to those who have served our country in the Armed Forces.
Attribution: Sean William per Creative Commons Attribution-Share Alike 3.0 Unported license.

Caption: Current version of the EpiPen, 0.3mg dose
Attribution: Author’s own work

The EpiPen probably has the largest share of the epinephrine autoinjector market, thanks to the efforts of Mylan. If you know someone who carries an epinephrine autoinjector, chances are pretty good they’re carrying the EpiPen. There are also more accessories specifically designed for the EpiPen, such as smart cases that link to a smartphone and provide a host of features such as notification of activation.

Mylan’s Authorized Generic Version of the EpiPen

Mylan now has an authorized generic version of the EpiPen. It’s exactly like the EpiPen except for the sticker/label put on the epinephrine autoinjector. According to the FDA, an authorized generic is EXACTLY like the brand name version, except the brand name doesn’t show up on the products label. You can see the below pictures to see how similar they look to the actual EpiPen:

Caption: Authorized generic versions of the EpiPen, 0.3mg (yellow) and 0.15mg (green) doses

One feature of the EpiPen is that after injection, the orange plastic tip will protrude from the bottom of the EpiPen so the needle is covered and not exposed to the user or anyone else.

Sanofi’s AUVI-Q

The AUVI-Q is the new kid on the autoinjector block, although it’s been on the market (off and on) for the past few years. It has three features that separates it from other epinephrine autoinjectors. First, it’s shaped like a really, really thick credit card. This shape can make it easier to carry around for some users.

Second, it talks and provides step-by-step prompts and information to users. According to Sanofi, the AUVI-Q has a higher percentage of successful use when users have little to no training. Basically, it’s a square shaped epinephrine autoinjector with a built in speaker.

Third, it comes in a 0.1 mg dose for infants and toddlers. Most of you reading this probably won’t need a dose this small, but it’s available for the small minority who might have a small one with a documented severe allergy.

Caption: Auvi-Q, the “talking” autoinjector in the 3 doses it’s offered in

Teva’s Generic Version of the EpiPen

At the time of writing, this may have only been on the market for a few weeks. It’s similar to the EpiPen in overall appearance and function, but there are two main differences.

First, it doesn’t come with a case. Instead, it has a cap covering the part where the needle comes out. Second, the blue safety release comes off in a slightly different manner.

Caption: Teva’s generic version of the EpiPen in both the 0.3mg and 0.15mg versions

Adamis Pharmaceutical’s SYMJEPI

I believe this one still hasn’t reached pharmacy shelves, but it’s really close from my understanding. Its main selling point is supposed to be its lower price than most epinephrine autoinjectors. The main reason for this is probably that it’s not really an autoinjector, but rather, a preloaded syringe.

Caption: The Symjepi (Note: may not be a picture of the final product)

To learn more about these various types of epinephrine autoinjectors, I recommended you check out Dr. Julie Brown’s Youtube page. She posts many videos showing most of these autoinjectors in action and other useful and interesting information relating to them.

Which One to Use?

That’s not an easy question to answer. Each one has its advantages and disadvantages, but what’s an advantage to one user may not be an advantage for another user.

For example, buying Teva’s EpiPen generic will save money, but for those who have hit their out-of-pocket limit on their health insurance, that feature won’t matter. Instead, they may still want the brand name EpiPen due to its familiarity to the general public and the greater number of accessories available (such as special cases). And when cost is a serious concern (such as those without insurance), the SYMJEPI might be the best option. However, it will not be an autoinjector and for those with a fear of needles or who might need others to assist in the injection, this could be a deal breaker.

As another example, if a young child has to carry an epinephrine autoinjector, the AUVI-Q might be the best one to use because of the high probability a teacher, childcare provider or complete stranger may be the one who will actually provide the epinephrine injection. The talking instructions could be crucial to an untrained individual.

Then there’s the availability of certain devices. Some pharmacies may have one version, but not the other. Anyone who needs to carry an epinephrine autoinjector should probably talk with their doctor and discuss their options. Some of these might be available directly from the pharmaceutical company for those who don’t have a nearby pharmacy that carries it.

Bottom Line

This blog post wasn’t intended (nor should it be interpreted) to provide a recommendation as to which epinephrine autoinjector to use. Rather, it hopefully provides more information so individuals can ask more informed question to their medical care providers.

Tuesday, October 23, 2018

Review: Oppama PET-304 Tach

If you want to objectively tune or troubleshoot your small two-stroke engine, you need a tachometer (tach). There are many options to choose from, but I choose to purchase Oppama Industry Co., Ltd.’s PET-304 since I saw some prominent lawn and small engine youtubers using it. I believe it’s also the same the Echo branded one, just without the Echo brand name stamped on it. Finally, I was also able to find a good deal: less than $62 shipped from Weingartz.

What’s in the Box?

I could tell you, but I’ll let my pictures do the talking:

Caption: This picture posts upside down for some reason.


RPM Range: 100 to 20,000 RPM
Accuracy: plus or minus 10 RPM
Accessories: Inductive pick up lead (included)
Weight: 29 grams
Updated readings: Every 0.5 seconds

Wired or Wireless?

When watching youtube videos of engine tachs, people simply hold the tach up to their engine and take a reading. But when searching online, most of the tachs have wires that attach the tach to the spark plug wire.

To clear up any confusion, you can take RPM readings with or without the wire. I choose to use the wire to get what I would presume would be more consistent readings. So instead of the holding distance varying depending on the engine and spark plug placement, I can just use the wire to make things more straightforward.

Caption: This is how the instructions say to connect the wire to the tach.
Attribution: Author’s Own Work
How Does it Work?

Exactly how you think it would. Just clamp the wire to the spark plug wire (ignition lead) and the tach will do the rest; it even turns on automatically when it’s close enough to the engine (1/2” to 12”) or is connected to the ignition lead.

There’s also no accessible battery compartment. Apparently this isn’t designed to have its battery replaced. Initially this bugged me, but the battery should last 20,000 hours. To put that in perspective, that’s more than 830 days of continuous use.

Here’s a picture of me taking a reading on an Echo PB-251

I also used it on my other machines, including my Echo CS-271T top handle chain saw and my Bolens BL110 string trimmer and it worked without issue.

Other Notes

Based on the pictures in the instruction manual, the PET-304 appears to be water resistant, so you can presumably use it in the rain without issue. However, the instructions also say to avoid getting the inductive lead wet or letting it touch anything during a reading. So if you want to use this in the rain, you’ll need to do so without the inductive lead. There is also a hour-meter function that keeps track of how long it’s been used.


Anyone in the market for a name brand, high quality tach should consider the PET-304. It’s a bit pricier than some models, but it’s a great addition to anyone’s toolbox or workshop.

Saturday, October 20, 2018

Project: Partial Restoration of the Echo PB-251

I love yardsaling and shopping at thrift stores and pawn shops where I can usually find a really good deal. For example, I got an operational Echo CS-271T for less than $85 out the door at my local pawn show (they were having a 50% off sale). Over the next few months I’ll take a close look at its condition to determine how great (or bad) of a deal I got. I will probably do a separate blog post on that chainsaw.

But for now, I want to discuss the Echo PB-251 blower I picked up at a yard sale for $5. Given its age, it was in decent shape. But it needed “a little bit of work” according to the seller. In this blog post I will share the rebuilding/refurbishing process of this blower.

In case you’re wondering, this is very similar to Echo’s current model, PB-250LN and they both have very similar specs: 142 mph v. 137 mph and 386 cubic feet v. 391 cubic feet.


I already had a Stihl backpack blower (BR 600 Magnum), but wanted a handheld for cleaning up grass clippings from my driveway (it’s annoying to lug around the backpack blower to run it for less than 5 minutes) and to increase my leaf blowing capacity in the fall. I saw some Stihl handheld blowers for around $65 to $90 at a few local pawn shops and thrift stores, but I wasn’t ready to pull the trigger on those for that kind of money.

Condition of the Echo PB-251 at Purchase

A picture is worth a thousand words, so I’ll begin by simply showing you what the PB-251 looked like when I bought it. It did come with the tube, but I removed it to take better pictures.

At first glance, I knew it required some muffler work and a new air filter. But besides that, I wasn’t sure what else was needed.

Did it Run?

Yes, yes it did. I reattached the muffler and it started up no problem. It also ran pretty well and was immediately useable as a blower. What I didn’t know was if it was running at its full potential. My only other gas powered leaf blower is my Stihl BR 600 Magnum and this handheld obviously could not compete with that backpack blower. But how was the PB-251 currently running compared to how it should be running? I did some digging and testing to figure that out.

The Muffler

The muffler was fine, but was missing the spark arrester screen. I bought an OEM replacement and installed it without a problem.

I also purchased two OEM bolts to hold the muffler cover on the blower (there’s a picture of the cover installed later in this blog post). At purchase, these bolts were missing and that’s why the above pictures of the blower don’t show the muffler cover (it wouldn’t say on).

From a performance perspective, this wasn’t necessary, but from a safety perspective, it was. I had already burned by finger once when I accidentally touched the hot muffler.

Caption: The bolts and spark arrester as they arrived from Echo’s parts supplier.
Attribution: Author’s Own Work


There was definitely some compression when I pulled on the rope, but having no prior experience with the PB-251, I had no idea if the compression was where it was supposed to be. My compression tester showed that it had about 120 PSI.

Caption: PB-251 compression reading.
Attribution: Author’s Own Work

Based on my online research, this is in the ballpark of what I should be getting. If anyone disagrees, please feel free to share by commenting.


According to the manual, the idle RPMs should be between 2,700 and 3,300, with wide open throttle at around 6,700 to 7,200. I tested this PB-2251 using my PET-304 Oppama tach (I’ll write a review blog post on this nifty little piece of kit soon) and measured 3,800 RPM at idle and 6,400 RPM at wide open throttle. I know these RPM readings don’t perfectly reflect an engine’s performance, but I wanted to get an idea of what I was getting without doing anything to the blower.

Also, the fuel I was using was old, I mean really old. It was mostly ethanol free 91 octane gasoline with Stihl Ultra 2 stroke oil from last fall (it’s about a year old during testing). So I would expect my numbers to be a little bit low.

Caption: RPM reading at idle before doing anything to the blower.
Attribution: Author’s Own Work

Cylinder and Piston

Given the compression and how the PB-251 ran, I was expecting the cylinder and piston to be in good shape. Based on my eyeball check after removing the muffler and spark plug, both looked to be in good shape with no signs of scoring. 

Spark Plug

Here’s a comparison of the old and new spark plugs. Looks like the old one’s been run a bit rich during its life.

Caption: The new one isn’t exactly like the old one, but it works.
Attribution: Author’s Own Work

Air Filter

The air filter was nasty and needed changing.

Caption: Can you guess which filter is the old one and which is the new one?
Attribution: Author’s Own Work

What’s interesting is that after installing the spark arrester and new spark plug, my wide open throttle RPM dropped to 5,800. My guess is that the spark arrester screen is largely responsible for this. But maybe the spark plug to? I’d be interested to hear any comments from anyone else on this issue.

After putting in the new air filter, it went back up to 6,400, so it looks like the old filter was as clogged as it looked!

The Rebuild Kit

In case you’re wondering, I got the new spark plug and air filter from some aftermarket seller on Amazon or eBay. It came with other things too, like a new carb, purge bulb, fuel filter and fuel lines. But since the blower seems to be in fine shape, I didn’t see a need to do the work of replacing those items.

Caption: In case you’re wondering about the kit’s number.
Attribution: Author’s Own Work

Caption: Here’s what’s in the box.
Attribution: Author’s Own Work

What Did it Cost?

Caption: The PB-251 with the muffler cover on it.
Attribution: Author’s Own Work

I spent a total of about $22 total on this blower ($5 for the blower and $17 for the rebuild kit). Since it works well enough already, I probably won’t do anything more to it. But this was a fun and easily little project that got me what is effectively a new handheld blower for less than $25.